The invention relates to an ultrasonic camera with a transmitter, an imaging system for an object and a receiver.
In a unit for the real-time representation of ultrasonic images of objects, electrical signals from a transmitter are changed in a converter into ultrasonic signals which penetrate the object to be imaged, which might be a part of the human body, and, as a general rule, are routed, with the aid of an imaging system, to a receiver which acts as an image sensor. The receiver might, for example, consist of a matrix of ultrasonic converters, which change the ultrasonic signals back into electrical signals, preferably into a charge pattern. The matrix is then scanned, line-by-line or column-by-column, and the image can be made visible on a video terminal assigned to the receiver (see, for example German patent document DE-OS No. 24 13 465).
The resolution of the image presented is inversely proportional to the frequency. In a B-scan, a high bandwidth is needed to generate short pulses. In a C-scan a high bandwidth is needed to suppress imaging errors resulting from the coherence of the sonic beam. A point element in the body level of the object that is to be imaged appears, with the aid of the imaging system, at the receiver as a local intensity distribution, whose width represents a parameter which is resolved by the camera. In the receiver, this ultrasonic distribution is converted into electrical signals by means of ultrasonic converters. It is preferable to select the expansion of the individual ultrasonic converters in the image level to be about half as large as the width of the intensity curve. The power of ultrasonic waves to penetrate body tissues is well known to depend on the frequency; high frequencies are more strongly absorbed in the object, and a corresponding displacement of the frequency spectrum is obtained at lower frequencies, with a simultaneous broadening of the intensity distribution.